 var Dog = new require("./dog.js");
 var dog1 = new Dog("taidy",4);
 var dog2 = new Dog("zangao",8);
 
 dog1.on("bark",() =>{
     this.bark();
 })
 dog2.on("bark",() =>{
    this.bark();
})


 setTimeI(() => {
     dog.emit("bark");
 }, 3000);